1. Field of the Invention
The present invention relates to a processing method for input audio signals, not only enabling a listener to obtain a feeling that he is located at an actual acoustic space actually containing a sound source or a feeling of localization of acoustic image even if he is not located at the actual acoustic space containing the sound source when he listens to a music with both the ears through ear receivers such as stereo ear phones, stereo head phones and various kinds of stand-alone type speakers, but also capable of realizing a precise localization of acoustic sound which has not been obtained with a conventional method.
2. Description of the Related Art
As a method for localization of acoustic image in, for example, listening to stereo music, conventionally, various methods have been proposed or tried. Recently, the following methods have been also proposed.
Generally it has been said that human being senses a location of a sound which he listens to or locations of up, down, left, right, front and rear with respect to a sound source relative to him by hearing the sound with his both ears. Therefore, it is theoretically considered that for a listener to hear a sound as if it comes from an actual sound source, by reproducing any input audio signal by real-time overlapping computation with a predetermined transmission function, that sound source can be localized in human hearing sense by the reproduced sounds.
According to the above described sound image localization system in the stereo listening, a transmission function for obtaining a localization of sound image outside the human head in auditory sense as if a person hears at an actual place containing a sound source is produced according to a formula indicating output electric information of a small microphone for inputting a pseudo sound source and a formula indicating an output signal of an ear phone. Any input audio signal is subjected to overlapping computation with this transmission function and reproduced, so that a sound from the sound source inputted at any place can be localized in auditory sense by reproduced sounds for stereo listening. However, this system has a disadvantage that the amount of software for computation processing and the scale of hardware will be enlarged.
Accordingly, in views of such a disadvantage that in the above conventional method for localization of sound image in stereo listening, the amount of software is increased and the scale of hardware is enlarged, the present invention has been achieved to solve such a problem, and therefore, it is an object of the present invention to provide a processing method for audio signal to be inputted from an appropriate sound source capable of higher precision localization of sound image than the conventional method.
To achieve the above object, according to an aspect of the present invention, there is provided a processing method for localization of sound image for audio signals for the left and right ears comprising, when a sound generated from an appropriate sound source is processed as an audio signal in the order of inputs on time series, the steps of: transforming the inputted audio signal to audio signals for the left and right ears of a person; dividing each of the audio signals to at least two frequency bands; and subjecting the divided audio signal of each band to a processing for controlling an element for a feeling of the direction of the sound source to be applied on person""s auditory sense and an element for a feeling of the distance up to the sound source and outputting the processed audio signal.
In the present invention, the element for a feeling of the direction of the sound source to be controlled is a difference of time of audio signals for the left and right ears, a difference of sound volume or the differences of time and sound volume. The element for a feeling of the distance up to- the sound source to be controlled is a difference of sound volume of audio signals for the left and right ears, a difference of time or the differences of sound volume and time.
Further according to another aspect of the present invention, there is provided a processing method for localization of sound image for the audio signal for the left and right ears comprising the steps of: dividing an audio acoustic signal inputted appropriately from a sound source to sounds for the left and right ears of a person; dividing the audio inputted signal of each ear to such frequency bands as low/medium range and high range, low range and medium/high range or low range, medium range and high range; and processing the audio signals for the left and right ears while the medium range band being subjected to a control based on simulation by a head portion transmission function of frequency characteristic, the low range band being subjected to a control with a difference of time or a difference of time and difference of sound volume as parameters, and the high range band being subjected to a control with a difference of sound volume or a difference of sound volume and the difference of time taken for combfilter processing as parameters.